Species Richness, Taxonomic Distinctness and Environmental Influences on Euphausiid Zoogeography in the Indian Ocean

Alicia Sutton,Lynnath Beckley

doi:10.3390/d9020023

Abstract

Although two thirds of the world’s euphausiid species occur in the Indian Ocean, environmental factors influencing patterns in their diversity across this atypical ocean basin are poorly known. Distribution data for 56 species of euphausiids were extracted from existing literature and, using a geographic information system, spatially-explicit layers of species richness and average taxonomic distinctness (AveTD) were produced for the Indian Ocean. Species richness was high in tropical areas of the southern Indian Ocean (0–20° S), and this high richness extended southwards via the Agulhas and Leeuwin boundary currents. In contrast, the land-locked northern Indian Ocean exhibited lower species richness but higher AveTD, with the presence of the monotypic family Bentheuphausiidae strongly influencing the latter result. Generalised additive modelling incorporating environmental variables averaged over 0–300 m depth indicated that low oxygen concentrations and reduced salinity in the northern Indian Ocean correlated with low species richness. Depth-averaged temperature and surface chlorophyll a concentration were also significant in explaining some of the variation in species richness of euphausiids. Overall, this study has indicated that the patterns in species richness in the Indian Ocean are reflective of its many unusual oceanographic features, and that patterns in AveTD were not particularly informative because of the dominance by the family Euphausiidae.

Highlights

Euphausiids are holoplanktonic, pelagic crustaceans inhabiting the world’s oceans from the surface waters to beyond the bathypelagic realm [1,2]
Environmental variables influencing euphausiid species richness have been investigated for the Pacific Ocean [11] and Atlantic Ocean [12]; sea surface temperature and Diversity 2017, 9, 23; doi:10.3390/d9020023
This study aims to: (1) determine zoogeographic patterns of euphausiids in the Indian Ocean using species richness and average taxonomic distinctness (AveTD); and (2) to use generalised additive modelling to determine environmental variables correlated with euphausiid species richness and AveTD in the Indian Ocean

Summary

Introduction

Euphausiids are holoplanktonic, pelagic crustaceans inhabiting the world’s oceans from the surface waters to beyond the bathypelagic realm [1,2]. There are 86 species of euphausiids, and they play an important role in the pelagic food web by consuming other plankton and by being a food source for higher order consumers, such as fishes, seabirds, and whales [3,4,5]. Euphausiids have been the subject of broad-scale zoogeographical studies as most extant species are expected to have been identified, and their distributions are relatively well known across the world’s oceans [6,7]. Environmental variables influencing euphausiid species richness have been investigated for the Pacific Ocean [11] and Atlantic Ocean [12]; sea surface temperature and Diversity 2017, 9, 23; doi:10.3390/d9020023 www.mdpi.com/journal/diversity

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